Polyoxometalates and peptides: hybridisation and disulfide detection

Damian, Heather Anne (2022) Polyoxometalates and peptides: hybridisation and disulfide detection. PhD thesis, University of Nottingham.

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Abstract

The structure of proteins and peptides determines their ability to perform their proper biological function. A key factor contributing to the tertiary structure formation are disulfide bridges. These bonds can increase a proteins resistance to extreme environments and have shown to protect protein-based therapeutics from rapid proteolytic degradation. Due to the importance of disulfide bonds in nature and therapeutics their detection and characterisation is significant.

Herein a novel colorimetric approach to investigate the redox state of biological disulfide bonds is explored, utilizing supramolecular metal-oxide nanoclusters (polyoxometalates) as soluble, redox-tunable probes. The ability to fine-tune the physicochemical properties of these clusters provides an exciting opportunity to create bespoke reducing agents which can be targeted to a specific substrate. The strong colorimetric response arising from the difference between the colourless oxidized (d0 ) state and the blue reduced (d1 ) states, provides a convenient and sensitive spectroscopic handle for ease-of-analysis. These states are attributed to the molecular poms addenda (M) atoms being found in either the (d1 ) or (d0 ) states. The technique development and experimental set up will be investigated and clarified.

As a proof of concept for this approach, two distinct polyoxoanions, [PW12O40] 3- and [H3W12O40] 5- , have been explored for use as redox probes by a combination of detailed theoretical, electrochemical, and spectroscopic analyses. Unlike existing analytical methods such as the classical Ellman’s test, the approach discussed herein is shown to be suitable for the direct interrogation of oxidised disulfide bonds. This is demonstrated for a range of model substrates. Herein is demonstrated the difference in reduction potential presented by the two POMs and their effects on commercial disulfides as well as two model peptides. These were synthesised through Fmoc-SPPS and then oxidised to form the disulfide bond. Characterisation of all the synthesised molecules was undertaken through NMR, CV, MS and HPLC.

Over the last decades polyoxometalates have demonstrated promising biological activities due to their diversity in structures and properties. The focus in the field of biologically active polyoxometalates lies on polyoxometalate-based nanocomposite structures and organically functionalised hybrids. These show enhanced antitumour activity and significantly reduced toxicity towards normal cell tissue in comparison to the parent polyoxometalates.

In this is explored the development of a novel linker system to attach to organic functional groups to a Wells-Dawson polyoxometalate. These linkers are based on bisphosphonate structures which are prevalent in a range of therapeutics, additionally there has been prior work done to show the synergistic effect of bisphosphonates couples to metal-oxide clusters. Three novel polyoxometalate-bisphosphonate linker molecular are formed and characterised using NMR and MS as well as identifying their absorption profiles under UV-vis light. Furthermore, the work progresses to demonstrate the use of the bisphosphonates as a handle for the attachment of amino acids to the hybrid structures. A selection of amino acids is explored, and then subsequent attachment of peptides is investigated. The peptides were synthesised via Fmoc-SPPS, purified via preparative HPLC, and characterised through MS and HPLC prior to addition to the linker systems.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Mitchell, Nicholas
Newton, Graham
Keywords: Polyoxometalates, Peptides, Hybridisation, Disulfide detection
Subjects: Q Science > QD Chemistry > QD450 Physical and theoretical chemistry
Faculties/Schools: UK Campuses > Faculty of Science > School of Chemistry
Item ID: 69268
Depositing User: Damian, Heather
Date Deposited: 02 Aug 2022 04:40
Last Modified: 02 Aug 2022 04:40
URI: http://eprints.nottingham.ac.uk/id/eprint/69268

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